Answer: The correct answer for the fill in the blank is External fertilization.
Most of the aquatic animals ( like fish) use external fertilization. Male and female release their sperm and eggs respectively in the free water where they are chemically attracted to each other in order to fuse.
Thus, the development of the embryo takes place outside the body ( in the water) of the mother. This means that mother does not carry the developing offspring in this case.
